A particularly preferred prior art filter cartridge and head unit is described in U.S. Pat. No. 4,735,716 to Petrucci et al, which is assigned to the same assignee as this application. This prior art filter cartridge and head unit includes a head, a cartridge, and securing means which secures the cartridge to the head. The head has a circular flat plate, which has an inlet port with an inlet passage, and which has an outlet port with an outlet passage. The cartridge has a housing, which has a cavity that contains filtering material, in order to pass a fluid from the inlet port, through the inlet passage, through the filtering material, and through the outlet passage to the outlet port. The securing means includes a pair of opposite tab receptacles, which are fixedly connected to the flat plate of the head and a pair of opposite tabs, which are fixedly connected to the housing which engage the respective tab receptacles by rotating the cartridge in one direction through 90 degrees and which disengage the respective tab receptacles by rotating the cartridge in an opposite direction through 90 degrees.
Related prior art patents include U.S. Pat. Nos:
3,852,196, to Szpur; PA1 3,746,171, to Thomsen; PA1 3,556,300, to Codo; PA1 3,358,839, to Simons; PA1 3,319,791, to Horne; PA1 2,979,208, to Humbert: and PA1 2,382,278, to Widmann.
U.S. Pat. No. 3,852,196 to Szpur describes a head, a cartridge and securing means. The head has a valve body, which has an inlet port with an inlet passage, and which has an outlet port with an outlet passage. The cartridge has a housing, which has a chamber that contains filtering material. The securing means includes an inner tubular portion, which is fixedly connected to the head and which has an exterior thread, and includes an outer tubular portion, which is fixedly connected to the cartridge, and which has an interior thread for engaging the exterior thread.
U.S. Pat. No. 3,746,171 to Thomsen describes a head, a cartridge, and securing means. The head has an inlet passage and an outlet passage. The cartridge has a housing which has a chamber that holds the filtering material. The securing means includes interacting cam portions.
U.S. Pat. No. 3,556,300 to Codo describes a head, a housing unit and securing means. The head has an elongate bolt disposed along a common axis of the head and housing. The housing has an upper inlet port and a lower outlet port. The housing and a filtering unit are mounted on the elongate bolt. The filtering unit is an annular unit forming an annular inlet chamber, and a central outlet chamber connecting to the outlet port. The annular filtering unit is supported on a cotter pin, which fits in a slot in the elongate bolt.
U.S. Pat. No. 3,358,839 to Simons describes a head or cap, a cartridge or elongate body, and securing means. The head has an outlet. The cartridge has a chamber, which contains a filtering sleeve, that has a top portion attached to the head. The securing means includes a pair of ridges which are fixedly connected to the head, and includes a pair of ridges with respective cam surfaces which are fixedly connected to the cartridge.
U.S. Pat. No. 3,319,791 to Horne describes a head, a cartridge and securing means. The head has an inlet port and an inlet passage, and has an outlet port and an outlet passage. The cartridge has a chamber which contains filtering material. The securing means includes a tubular portion, which is fixedly connected to the head and which contains an internal thread, and includes a stem portion, which is fixedly connected to the cartridge and which has an exterior thread for engagement with the interior thread.
U.S. Pat. No. 2,979,208 to Humbert describes a head, a cartridge, and a securing means. The head has an inlet port and an outlet passage. The cartridge has a chamber, which has an annular filtering element, that forms an outer annular space connecting to the inlet passage and forms an inner space connecting to the outlet passage. The securing means includes a tubular lower portion, which is fixedly connected to the head and which has an exterior thread, and includes a ring portion which is fixedly connected to the cartridge and which has an interior thread for engagement with the exterior thread. The tubular lower portion has a locking screw which has an end portion that bears against the ring portion when the screw is rotated clockwise, in order to prevent unscrewing the cartridge from the head.
U.S. Pat. No. 2,382,278 to Widmann describes a head, a cartridge and securing means. The head has an inlet port and an inlet passage, and has an outlet port and an outlet passage. The cartridge has a chamber, which contains an annular filtering element that forms an outer annular space connecting to the inlet passage, and forms an inner space connecting to the outlet passage. The securing means includes a tubular lower portion, which is fixedly connected to the head and which has an interior thread, and includes a ring portion, which is fixedly connected to the cartridge and which has an exterior thread for engagement with the interior thread. The tubular lower portion has an ear portion with a first hole and the ring portion has a portion with a second hole, and a locking wire extends through the first hole and the second hole in order to prevent unscrewing the cartridge from the head.
One problem with the prior art filter cartridges and head units is that it is possible for a person, or a child, to rotate the filter cartridge relative to the head. This will cause the securing tabs of the cartridge to disengage from the securing tab receptacles of the head causing the filter to be driven out of the head by the normal line pressure, thereby allowing the escape of fluid under pressure. In the case of the usual fluid dispensing machine, where the head is fixedly attached to the underside of the dispensing machine, or the like, a securing means which requires a locking wire or locking screw, also requires special tools and is not easily accessible.